The invention relates to an exposure device for exposing a projection of an electronically stored artwork pattern onto a substrate, in particular a printing plate, with image processing electronics that can store the image data, with a light modulator that can be electronically controlled by the image processing electronics, in particular an LCD display or a micro-mirror device, with an illuminating device for illuminating the light modulator and with a projection lens for projecting the light modulator onto the substrate. The invention also relates to a method for compensating for optical defects and/or tolerances in the beam path of such an exposure device.
An exposure device of this kind, which is used to expose printing plates with ultraviolet light, is known from DE 195 45 821 A1, for example. In this instance, the artwork pattern to be projected is broken down into partial images by a computer and the partial images are cast one after the other onto an electronically controllable light modulator, for example an LCD display through which radiation passes or a micro-mirror device. The exposure device is then gradually moved across the printing plate to be exposed, the light modulator being respectively triggered with the appropriate partial image. Micro-mirror devices, also referred to as digital mirror devices or DMD for short, are comprised of an arrangement of tiny mirrors with edge lengths of a few micrometers on the surface of an electronic chip, in which each individual mirror can be individually tilted by being electronically triggered so that an incident light beam can either be directed into a projection objective or directed past it, depending on the tilting angle of the mirror.
Due to optical defects and tolerances in the beam path of the exposure device, the projection exposed on the substrate to be exposed, in particular a printing plate, deviates from the electronic artwork pattern. In particular, shadows are produced at the edges and in the corners of the individual images.